In the case of shearer loaders, rack arrangements are used for the feeding of the shearer loader, said rack arrangements usually being mounted on scraper chain conveyors arranged and laid at the underground longwall face, wherein the shearer loader, as winning machine, can be supported on the supporting strips by means of guide shoes and can at the same time be guided on the guide shoes. The teeth of the sprockets of the travel drive engage in the tooth gaps between the rack teeth in order to convert the rotational movement of the sprocket into a translational movement of the shearer loader. The rack arrangement is usually composed of rack bars, the length of which corresponds substantially to the length of a respective pan section of the scraper chain conveyor so that the scraper chain conveyor and in this respect also the machine track together with rack can conform to an undulating course of the winning longwall face with synclines, anticlines and curves. Due to the segmental construction of the rack arrangement on account of the individual rack bars, a shearer loader can also follow a curved course of a face conveyor and the horizontal and/or vertical bends without obstruction. In the operational use of shearer loaders, the rack bars and the entire feed system are subjected to considerable and also alternating stresses, since shearer loaders usually travel under load, but also sometimes without load, along the rack formed by the rack bars.
A feed system of the generic type having associated rack bars is known from DE 197 46 360 A1. The known feed system is successively used by the applicant under the trade name “JUMBOTRACK” or “JUMBOTRACK 2000” for a shearer loader for extracting coal in underground mining. In the rack arrangement of the generic type according to DE 197 46 360 A1, the individual rack teeth have been given special tooth profiling for improving the feed of the shearer loader and the tooth engagement relationship between the teeth of the drive sprocket and the rack teeth, said tool profiling being characterized in that the tooth flanks of adjacent rack teeth, said tooth flanks diverging relative to one another towards the tooth tip, have a relatively planar flank surface which runs inclined at an angle of about 8° to 15°, preferably 10° to 12°, to the tooth centre plane of the individual rack teeth. Owing to the fact that the tooth flanks of the rack teeth are designed as planar and steeply inclined surfaces, lifting of the winning machine on account of transverse force components and the disturbing influences resulting therefrom can be suppressed to the greatest possible extent. In order to cope at the same time with problems at the joints between adjacent rack bars, asymmetrical end teeth are used at both ends of the rack bars of the known feed system, in which end teeth the tooth flank facing the inner rack teeth is given respective tooth flank profiling which runs at a steeper angle relative to the vertical than the respectively outer tooth flank, i.e. the tooth flank facing the joint of adjacent rack bars. Due to the asymmetrical configuration of the end teeth, the tooth pitch of the rack bar in each case between two end rack teeth or end teeth of adjacent rack bars will be increased slightly compared with the standard tooth pitch.
Increasing wear in particular on the tooth shape of the drive sprocket can also occasionally occur after a long operating period in the case of the rack arrangement according to DE 197 46 360 A1. The teeth of the sprocket drive are in principle subjected to higher loads than the rack teeth since the feed forces have to be transmitted by the teeth of the drive sprockets, and the engagement of each individual tooth with a rack tooth occurs much more frequently that the loading of an individual rack tooth overall.